Switch control system



July 16, 1940. Q'HAGAN 2,208,429

SWITCH CONTROL SYSTEM Filed Sept. 22, 193B lNV TOR Bop/2am! Hagan. BY

HIS ATTORNEY Patented July 16, 1940 2,208,429

UNiTED STATES PATENT OFFICE SWITCH CONTROL SYSTEM Bernard E. OHagan, Swissvale. Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 22, 1938, Serial No. 231,229 6 Claims. (01. 246-242) My invention relates to a control system for A further object of my invention is to provide the motor for operating a railway track switch. an improved switch motor control system.

It has heretofore been proposed to provide an Other objects of my invention and features of overload relay having a winding energized in novelty will be apparent from the following deaccordance with the current taken by the motor, scription taken in connection with theaccom- 6 and having a contact which becomes picked up panying drawing. when the motor current exceeds a predetermined In the drawing the single figure is a diagramvalue for longer than a predetermined time. The matic View showing one system embodying my overload relay contact when picked up effects ininvention. terruption of the motor circuit to prevent injury Referring to the drawing, the reference char- 10 to the motor. acter W designates a railway track switch which It has also been proposed heretofore to provide s Ope by the Well-known dual Selector yp a holding winding either as a part of the overof mechanism. In the form here shown dia load relay or as a part of a separate relay, this grammatically this mechanism includes a dual winding being energized on picking up of the selector lever S which operates a link 3. When overload relay contacts and being operative when the dual selector lever S is in the normal posienergized to establish a circuit to maintain itself tiOn, as ShOWn in h drawing, link 3 Connects energized. This winding controls means which switch W with the motor M, while when the lever operates when the winding is energized to main- S is in the reverse D0Siti011,-1ink 3 no longer min th energizing i it f t Switch motor connects the switch W to motor M but instead 20 '40 contacts in order to effect interruption of the device provided with a movable member interrupted connects the switch to a hand-throw lever H.

It has been proposed to provide means operable The Switch W operates a motor ut 60nwhen the dual selector lever is in the hand-throw toot 5 in accordance With the P on of the position to energize the holding winding and thus Switoh- The Contact 5 is arranged S0 that it enprevent operation of the switch motor while the gages a Contact 6 in all positions of e Switch 5 dual selector lever is in the hand-throw position W except the normal Position thereof, d S0 7 or until such time thereafter that the position that it engages a Contact 7 in all positions of the of the Switch control lever is changed. switch W except the reverse position thereof.

The arrangement heretofore employed i u h" 'I'hE dual Selector lever S Operates Contacts 9 however, that the holding winding will operate to and m in such a manner that when the dual to effect interruption of the switch motor circuit selector lover is in the normal position t is only as long as the winding is energized and if the position in which it is shown and in which it for any reason the supply of current to the wind- .oonditlons the switch W for Operation y the ing is interrupted the holding winding will fail motor M, Contact 9 engages Contacts 12 and I 3,

to prevent operation of the switch motor. while Contact to engages contacts '4 and 5- In It is an object of my invention to provide a the hand-throw position of the dual selector lever control System including a relay having a wind s the contacts 9 and [0 do not engage the staing which is normally energized, and which is tionory contacts associated therewith deenergized on picking up of the overload relay The control system includes a suitable control Switch motor circuit ment having a normal position in which it es- A f rther Object of my invention is to provide tablishes circuits for the switch motor to cause an improved control System of the described the motor to move the SWltCh t0 the normal 1305iand incorporating means operable on movement tion, this member or element also having a e- 5 or th dual l t l v t t hand throw p051- verse position in which it establishes circuits for tion to effect deenergization of the said winding the Switch motor to Cause th mo or to move the and thus interrupt the switch motor circuit. Switch to the reverse P O Another object of my invention is to provide As ShOWh in the drawing, s control device I a control system of the type described and arcomprises a Polarized Switch Control relay WR,50

ranged so that on deenergization of the winding having a Winding which is energ ed y u ent mentioned above it will not again become enersupplied over control wires 20 and 2|. The relay gized until the dual selector lever is returned to WR has an armature which operates contacts its normal position and the position of the switc 23, 24. and 25, while the armature is movable control lever is thereafter changed. between a normal and a reverse position in ac- Iii locking tower, operates contacts 2'! and 28 t control the polarity of the current supplied from a battery 30 to control wires 28 and 2!. When the control lever L is in the normal position, as shown, contact 21 connects control wire 25 to terminal 'B of a battery 55 and contact 28 con nects control wire 3! to terminal C of the bat tery 30 to thereby effect the supply of current of normal relativepolarity to the control wires 25 and 2!.

When the control lever L is in the reverseposi tion, contact 21 connects control wire 28 to terminal C of battery 3i), while contact 28 connects control wire 2i to terminal B of battery 35 to thereby efi'ect the supply of current of reverse relative polarity to the control wires 20 and 2!.

The polar contact 23 of relay WR. is connected by a wire 32 to one brush of the motor armature 33.01 the switch motor M, while polar contact 24 is connected by a wire 35 to the other brush of the motor armature.

Polar contact 23, when in its normal position as'shown, engages a normal polar contact 31 which is connected by wire 38 to stationary con-, tact l5, while a branch ofwire 38 is connected to reverse polar contact 39 whichis adapted to be engaged by a polar contact 24. Stationary contact i is engaged by movable contact H1 in 5 the normalposition of the selector lever S, while the contact ill also engages stationary contact I4 which is connected by wire 40 to terminal B of battery 42.

tact 1 which at times is engaged by the switch operated contact 5. In similar manner, polar contact 24 of relay WR, when in its normal position as shown, engages normal polar contact 41, which is connected by wire 48 to stationary contact 6 which is engagedat times by switch oper ated contact 5.

Switch operated contact 5 is connected by Wire 49 to one terminal of the field winding 50 of the motor M, while the other terminal of the winding 50 is connected by a wire 5| to one terminalof a resistance unit 53 and to one terminal of the winding of the overload relay OR. The other terminal of the resistance unit 53 and of the winding of the overload relay OR are connected by a wire 55 to a contact 56 of relay ORPP A branch of wire 55 is connected to movable contact 58 of relay 0R, while the contact 58 when released engages stationary contact 59 which is connected by a wire 60 to one terminal of the winding of relay ORB.

The resistance unit 53 has a positive thermal coefficient of resistance, that is the; resistance of the unit increases as the temperature of the material of which the unit is constructed increases. The resistance unit 53 and the over- '-load relay OR are arranged and proportioned so ,that under normal operating conditions most of the current flowing in the circuit of the switch motor flows through the resistance unit 53 and too little current flows in the winding of the relay OR to cause the contact 58 to be picked up. SAccordingly, contact 58 remains released.

0n flow of an unusually heavy current in the circuit of the switch motor for an abnormally long time interval, such as occurs when move- The contact 25 of relay WR controls a circuit for energizing the winding of the relay ORP. Contact 25 is operated by the armature of the polar relay WR. and is of the make-before-break type. When the relay armature is in the normal position, as shown, contact 25 engages normal polar contact 66 to which is connected a branch of wire Mleading from terminal C of battery 42,

and when the relay armature is in thereverse position, the contact engagesa reverse polar contact 68 to which is connected a branch of wire 55.

The movable contact 25 and the stationary contacts 56 and 68 are arranged and constructed so that on movement of the armature of the relay WR from its normal position to its reverse position, the contact 25 will engage contact BB'before it is moved out of engagement with contact 66. Similarly, on movement of the relay armature from its reverse to its normal position, the contact 25 will engage contact 56 before it is moved out of engagement with contact 58. It will be seen, therefore, that on movement of the relay armature from one of its positions to the other,

there is a brief time interval in which the movable contact 25 is in engagement with the contacts 66 and 58 to thereby establish a circuit from wire 64! leading from terminal C of battery 52 to wire 55 leading to one terminal of the winding of relay ORP.

The equipment isshown in the drawing with the switch W, the control lever L, and the dual selector lever S in their normal positions, with the overload relay OR, releasedand with the relay ORP energized. As the control lever L is in the normal position, current of normal relative polarity is supplied to the control wires 20 and 2| and the polar contacts of the relay WR are in their normal positions, While the circuit for energizing the switch motor M is interrupted by the switch operated contact 5.

At this time the contact 58 of relay OR, is released and the winding of relay ORP is energized by current supplied over a circuit which is traced from terminal B of battery 32 through wire 4!], dual selector lever contact 9, wire 6!, winding of relay ORP, wire 56, contacts 59--58 of relay OR, wire 55, contacts 55fi2 of relay ORP and wire 64 to terminal C of battery 42.

If at this time the operator wishes to eiTect movement of the switch W from its normal to its reverse position, he may do so by moving the con trol lever L from its normal to its reverse position. 'On this movement of the control lever L, the contacts 21 and 28 are operated to effect the supply of current of reverse relative polarity from battery to control wires 2!! and 2!, and on the supply of energy of this relative polarity, the polar contacts of relay WE are moved from their normal positions to their reverse positions to thereby establish a circuit to energize the switch motor M to cause it to move the switch to the reverse position.

' The energizing circuit for the switch motor M \is traced from terminal B of battery 42 through wire 46, dual selector lever contact l6, wire 38, reverse polar contacts 39-24 of relay WR, wire 35, motor armature 33, wire 32, reverse polar contacts 23-44 of relay WR, wire 45, contact I, iswitch operated contact 5, wire 49, motor field winding 50 wire 5|, resistance unit 53 and winding of relay OR. in multiple, wire 55, contacts 56-62 of relay ORP, and wire 64 to terminal of battery 42. i

As a result of this supply of current to the motor M, the switch W is caused to move to the reverse position and when it reaches the reverse position, contact is moved out of engagement with contact 1, thereby interrupting the circuit for energizing the switch motor.

In like manner, if when the switch W is in the reverse position the operator desires to move it to the normal position, he may do so by returning the control lever L from its reverse to its normal position. On this movement of the lever L, the contacts 21 and 28 are operated to supply current of normal relative polarity to the control wires and 2|, and the polar contacts of relay WR are caused to move to their normal positions as shown, thereby establishing circuits to energize the switch motor M to cause it to move the switch W from the reverse to the normal position.

The energizing circuit for the switch motor M is traced from terminal B of battery 42 through wire 40, selector lever contact l6, wire 38, normal polar contacts 31-23 of relay WR, wire 32, motor armature 33, wire 35, normal polar contacts 24-41 of relay WR, wire 48, contact 6, switch operated contact 5, wire 49, field winding of switch motor M, wire 5|, resistance unit 53 and Winding of relay OR in multiple, wire 55, contacts 56-62 of relay ORP, and wire 64 to terminal C of battery 42.

As a result of this energization of the switch motor M, the switch W is moved from the reverse to the normal position and when the switch reaches the normal position, contact 5 is moved out of engagement with contact 6 to thereby interrupt the energizing circuit for the switch motor.

This control system is arranged so that if while the switch W is being moved from one of its positions towards the other of its positions further movement of the switch is prevented bethat the switch W is being moved from the normal to the reverse position and that further movement of the switch is prevented before the switch reaches the reverse position.

On the occurrence of the obstruction to movement of the switch, there is an increase in the flow of current in the circuit of the switch motor and therefore in the resistance unit 53. When this increased flow of current has continued for a predetermined length of time, the temperature of the resistance unit 53 is increased to such an extent that the resistance of the unit increases and causes a sufficient increase in the flow of current in the winding of the relay OR sufficient to effect picking up of the contact 58 of the relay OR.

- On picking up ofthe contact 58 of the relay OR, the circuit for energizing the winding of relay ORP is interrupted, and contact 62 of relay ORP becomes released to interruptthe energizing circuit for the switch motor M. On interruption of the circuit of the switch motor, current is no longer supplied to the winding of the relay OR and contact 58 of this relay becomes released to again engage contact 59. However, on release of contact 58, the circuit for the winding of relay ORP is not reestablished since contact 62 of relay ORP is released, thereby interrupting the circuit from terminal C of battery 42 to contact 58.

If following the interruption of the switch motor circuit due to an obstruction of the switch the operator wishes to return the switch to the position from which it Was being moved when the obstruction occurred, he may do so by returning the control lever L to its former position, in this case the normal position. As a result of this movement of the control lever L, current of normal relative polarity is supplied to the control wires 26 and 2| and the polar contacts of the relay WE are moved to their normal positions to establish circuits to energize the I switch motor M to cause it tomove theswitch the other, contact 25 will be in engagement withboth contact 66 and contact 68 for a time interval. When contact 25 engages both of the contacts 66 and 68, a circuit is established to energize the Winding of relay ORP, this circuit being traced from terminal B of battery 42 through wire 40, selector lever contact 9, wire 6|, winding of relay ORP, wire 60, contacts 59-58 of relay OR, wire to reverse polar contact 68 of relay WR, contact 25, normal polar contact 66, and wire 64 to terminal C of battery 42.

The equipment is arranged so that on move- 5 ment of the armature of the relay WR between its two positions, the contact 25 establishes a circuit between contacts 66 and 68, and thereby energizes the winding of relay ORP, for a long enough period of. time to efiect picking up of contact 62- of the relay. On picking up of contact 62, a stick circuit is provided for the winding of relay ORP to maintain the winding energized after contact 25 ceases to establish connection between contacts 66 and 68. The stick circuit includes wire 64, contacts 62-56 of relay ORP, wire 55, contacts 58-59 of relay OR, and wire leadingto a terminal of the winding of relay ORP. On picking up of contact 62, the energizing circuit for the switch motor M is complete, and the polar contacts of the relay WR being in their normal positions the switch motor M is energized in a manner to cause it to move the switch W to the normal position.

In similar manner, if while the switch is in the reverse position and is being moved to the normal position movement of the switch is obstructed, contact 58 of the overload relay OR will interrupt the circuit for the winding of the relay ORP, and relay ORP will thereupon interrupt the switch motor circuit and thus prevent injury to the switch motor. The switch W may then be returned to the reverse position by mov ing the switch control lever Lto the reverse position, while on this reversal of the polarity of the current supplied to the control wire, the

armature of the relay WR will be moved to its reverse position and contact 25 will momentarily establish a circuit to energize the Winding of relay ORP, and thus reestablish the switch motor circuit in the manner just described in detail.

The control system provided by thisinvention is arranged in such a manner that on movement of the dual selector lever S to the hand-throw position, the winding of the relay ORP is deenergized, thereby interrupting the circuit of the switch motor, and so that on return of the dual selector lever to the normal position, the winding of the relay ORP will not again become energized until there is a change in the position of the control lever L subsequent to return of the dual selector lever S to the normal position.

On movement of the dual selectorlever S to the hand-throw position, contacts 9 and H! are moved out of engagement with the stationary contacts associated therewith. On movement of contact 9 out of engagement with contacts l2 and 13, the circuit from terminal B of battery 42 through wire 6| leading to a terminal of the winding of relay ORP is interrupted and contact 62 of relay ORP becomes released, thereby inter! rupting the switch motor circuit at one point. In addition, on movement of contact In outof engagement with contacts I4 and I5, the connection from wire 40 leading from terminal B of battery 42 to wire 38 is interrupted, thereby interrupting the energizing circuit of the switch motor M at another point. It will be seen, therefore, that as long as the dual selector lever S is in the hand-throw position, the switch motor circuit is interrupted and the switchmotor M cannot be energized to cause movement of the switch On return of the selector lever S to the normal position, contact Ill is moved into engagement with contacts I4 and I5, thereby reestablishing the circuit from wire 48 to wire 38. However, the energizing circuit for the switch motor continues to be interrupted at this time since contact 62 of relay ORP is released.

On return of selector lever S to the normal position, contact 9 again establishes connection between contacts I2 and [3 to thereby establish a circuit from terminal B of battery 42 to wire 6| leading to one terminal of the winding of relay ORP. However, at this time no connection is established from wire 60, leading from the other terminal of the winding of relay ORP, to terminal C of battery 42 and hence the winding of relay ORP does not become energized. A circuit is not established from wire 50 to terminal C of battery 42 since contact 62 of relay ORP is released and since contact 25 of relay WR. does not bridge contacts 66 and 68.

It will be seen, therefore, that on return of the selector lever S to the normal position, a circuit is not reestablished to energize the winding of relay ORP and contact 62 continues to interrupt the circuit for energizing the switch motor M.

The winding of the relay ORP will become energized, however, as soon as there is a change in the position of the control lever L, and therefore in the position of the polar contacts of relay,

On a change in the position of the control lever L and consequent reversal in the polarity of the current supplied to the control wires 20 and 2|, the polar contacts of relay WR are shifted from one position to the other, and during this movement of the polar contacts, contact 25 mo-v mentarily bridges contacts 66 and 68, thereby establishing a circuit from wire 64, leading from, terminal C of battery 42, to wire 55 which is connected by contacts 5859 of relay OR to wire Gil leading to a terminal of winding ORP. The winding of relay ORP, therefore, is energized and contact 62 becomes picked up to establish a stick circuit for the relay winding and to complete the circuit for energizing the switch motor. If at this time the switch W and the control lever L areout of correspondence, the switch motor M will move the switch W- to the position corresponding to that occupied by the control lever L. Similarly, if at the time the contact 62 of relay ORP becomes picked up, the switch W and the lever L are in correspondence, the energizing circuit for the switch motor will be interrupted by switch operated contact 5 and the motor, therefore, willnot be energized and will not move the switch.

From the foregoing it will be seen that on movement of the selector lever S from the normal position to the hand-throw position, the relay ORP is operated to remove the switch motor M from control of the control lever L, and that on return of the selector lever S to the normal position, the relay ORP is not conditioned to restore control of the switch motor to the control lever L until there is a change in the position of the control lever L. This mode of operation is desirable as it insures that if, While the selector lever is in the hand-throw position, the position of the control lever L is changed, then on return of the selector lever S to the normal position the switch motor M will not be energized to effect movement of the switch W to the position corresponding to that occupied by the control lever L. There is, therefore, no storage of switch control while the selector lever S is in the handthrow position.

In addition, it will be seen that the relay'ORP is conditioned to establish the switch motor cirit interrupts the circuit for the switch motor.

Accordingly, if for any reason the winding of the relay ORP is not energized at a time when it should be energized, the relay contact will open and will interrupt the switch motor circuit to prevent undesired operation of the switch motor as long as the winding of relay ORP remains deenergized.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without detparting from the spirit and scope of my invenion.

Having thus described my invention, what I claim is:

1. In a switch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a control device having a movable member having anormal position and a reverse position, the movable member being operable in the normal position to establish a normal supply circuit through which current may be supplied to the motor to cause it to move the switch to the normal position, said movable member being operable in the reverse position to establish a reverse supply circuit through which current may be supplied to the motor to cause it to move the switch to the reverse position, means for effecting movement of the control device movable member between its two positions, an auxiliary relay having contacts included in said motor supply circuits, said contacts being closed when and only when the winding of the said relay is energized, a holding circuit for energizing said auxiliary relay winding, said holding circuit including contacts of said relay closed when and only when the relay winding is energized, the control device movable member having associated therewith mechanism actuated by movement of the said member from one of its positions to the other to also establish a circuit for energizing the winding of the auxiliary relay, said mechanism being ineffective to establish such circuit for the winding of the auxiliary relay when the control device movable member is in either its normal or its reverse position, and means responsive to the magnitude of the current taken by the switch motor for interrupting the auxiliary relay holding circuit.

2. In a switch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a control device having a movable member having a normal position and a reverse position, the movable member being operable in the normal position to establish a normal supply circuit through which current may be supplied to the motor to cause it to move the switch to the normal position, said movable member being operable in the reverse position to establish a reverse supply circuit through which current may be supplied to the motor to cause it to move the switch to the reverse position, means for effecting movement of the control device movable member between its two positions, an auxiliary relay having contacts included in said motor supply circuits, said contacts being closed when and only when the winding of the said relay is energized, a holding circuit for energizing said auxiliary relay winding, said holding circuit including contacts of said relay closed when and only when the relay winding is energized, the control device movable member having associated therewith mechanism operable during movement of the said member from one of its positions to the other to also establish a circuit for energizing the winding of the auxiliary relay, said mechanism being inefiective to establish such circuit for the winding of the auxiliary relay when the control device movable member is in either its normal or its reverse position, a dual selector lever movable from a normal positionin which it conditionsthe switch for operation by the motor to a hand-throw position in which it conditions the switch for manual operation, and means operative on movement of said lever from the normal position to interrupt the auxiliary relay holding circuit.

3. In a switch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a control device having a movable member having a normal position and a reverse position, the movable member being operable in the normal position to establish a normal supply circuit through which current may be supplied to the motor to cause it to move the switch to the normal position, said movable member being operable in the reverse position to establish a reverse supply circuit through which current may be supplied to the motor to cause it to move the switch to the reverse position, means for eiiecting movement of the control device movable member between its two positions, anauxiliary relay having contacts including in said motor supply circuits, said contacts being closed when and only when the winding of the said relay is energized, a holding circuit for energizing said auxiliary relay winding, said holding circuit including contacts of said relay closed when and only when the relay winding is energized, the control device movable member having associated therewith mechanism operable during movement of the said member from one of its positions to the other to also establish a circuit for energizing the winding of the auxiliary relay, said mechanism being inefiective to establish such circuit for the winding of the auxiliary relay when the control device movable member is in either its normal or its reverse position, means responsive toIthe magnitude of the current taken by the switch motor for interrupting the auxiliary relay holding circuit, a dual selector lever movable from a normal position in which it conditions the switch for operation by the motor to I a hand-throw position in which it conditions the switch for manual operation, and means operative on movement of said lever from the normal position to also interrupt the auxiliary relay holding circuit.

4. In a switch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a pair of conductors, means for supplying current of one relative polarity or the other to said conductors, a polarized relay energized from said conductors, said relay having polar contacts having ,a normal position in which a normal supply circuit is established through which current may be supplied to the motor to cause it to move the switch to the normal position, said polar contacts also having a reverse position in which a reverse supply circuit is established through which current may be supplied to the motor to cause it to move the switch to the reverse position, an auxiliary relay having contacts included in said motorsupply circuits, said contacts being closed when and only when the relay winding is energized, the polarized relay having make-beiore-break contacts closed only during movement of its polar contacts between their normal and reverse positions to: establish a pick-up circuit for energizing the winding of the auxiliary relay, a holding circuit for energizing the auxiliary relay winding, said holding circuit including contacts of said auxiliary relay closed when and only when the winding of said relay is energized, and means responsive to the magnitude of the current taken by said motor for interrupting the auxiliary relay holding circuit.

5. In a switch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a pair of conductors, means for supplying current of one relative polarity or the other to said conductors, a polarized relay energized from said conductors, said relay having polar contacts having a normal position in which a normal supply circuit is established through which current may be supplied to the motor to cause it to move the switch to the normal position, said relay polar contacts having a reverse position in which a reverse supply circuit is established through which current may be supplied to the motor to cause it to move the switch to the reverse position, an auxiilary relay having contacts included in said motor supply circuits, said contacts being closed when and only when the relay winding is energized, the polarized relay having contacts closed when and only when its polar contacts are being moved between their normal and reverse positions to establish a pickup circuit for energizing the winding of the auxiliary relay, a' holdingcircuit for energizing the auxiliary. relay winding, said holding circuit including contacts of said relay closed when and only. when the winding of said relay is energized, a dual selector element movable between a normal position in which it conditions the switch for operation by the motor and a hand-throw position in which it conditions the switch for manual operation, and means controlled by said element and operative in the hand-throw position thereof to interrupt the auxiliary relay holding circuit, said means being operative in the normal position of said element to establish a circuit through whichcurrent may be supplied to the auxiliary relay winding.

6. In aswitch control system, in combination, a railway track switch movable between a normal and a reverse position, a motor for moving said switch, a pair of conductors, means for supplying current of one relative polarity or the other cause it to move the switch to the normal position, said polar contacts having a reverse position in which a reverse supply circuit is established through which current may be supplied to the motor to cause it to move the switch to the reverse position, an auxiliary relay having contacts included in said motor supply circuits, said contacts being closed when and only when the relay winding is energized, the polarized relay having contacts closed when and only when its polar contacts are being moved between their normal and reverse positions to establish a pick-up circult for energizing the winding of the auxiliary relay, a'holding circuit for energizing the auxiliary relay said holding circuit including contacts of said auxiliary relay closed when and only when the winding of said relay is energized, means responsive to the magnitude of the current taken by said motor for interrupting the auxiliary relay holding circuit, a dual selector element movable between a normal position in which it conditions the switch for operation by the motor and a hand-throw position in which it conditions the switch for manual operation, and means controlled by said element and operative in the hand-throw position thereof to interrupt the auxiliary holding circuit relay, said means being operative in the normal position of said element to establish a circuit through which current may be supplied to the auxiliary relay winding.

BERNARD Ol-IAGAN. 

